1. Field of the Invention
The invention relates to a method of manufacturing a compound semiconductor device using GaN related materials. More particularly, the invention is directed to an improved connection of electrodes to an n-type semiconductor layer in the device. The compound semiconductor device using GaN related materials includes, e.g., light-emitting diodes and laser diodes.
2. Description of the Related Art
The compound semiconductors such as GaN related materials, being of a direct transition type, exhibit high light-emitting efficiency and emit blue light, which is one of the three primary colors of light. Therefore, the compound semiconductors such as GaN related materials attract attention as a light-emitting device forming material in recent years.
In such the compound semiconductor device such as a GaN related meterials, a material for n electrode that is connected to an n-type semiconductor layer generally requires a low work function. Aluminum (Al) has exclusively been used as the n electrode forming material.
The n-type semiconductor layer in a light-emitting diode using GaN related materials generally becomes a first clad layer, on which a light-emitting layer and a p-type semiconductor layer serving as a second clad layer are sequentially grown. Then, some part of the p-type semiconductor layer, the light-emitting layer, and the n-type semiconductor layer is introduced to a reactive ion etching process using a gas or the mixing gas with at least a gas containing either chloride or fluorine atom to thereby form a forming portion for electrode on the n-type semiconductor layer.
Since it is assumed that the surface of n-type layer which is etched by RIE process is deposited by remnants such as chlorides and oxides which are formed at the etching process, the portion for electrode has been further introduced to a sputtering process (hereinafter referred to as the "after treatment") using an inert gas such as argon as disclosed in Japanese Patent Publication No. Hei. 3-108779.
An n electrode is formed by depositing Al onto the thus after-treated electrode forming portion.
The inventors have studied the thus formed element. As a result, the inventors have found that such element addresses the following problems to be overcome.
If the after treatment is omitted, it is difficult to obtain good ohmic contacts between the semiconductor layers and the n electrode. However, even if an after treatment is carried out, the ohmic contacts are hard to stabilize. That is, the resistance between the semiconductor layers and the n electrode fluctuates. The reason therefor is assumed to be that remnants deposited the portion for electrode are hard to remove completely even if an after treatment is carried out.
If an after treatment is to be carried out, a step must be added to in the manufacturing process. In order to remove the remnants deposited on the portion for electrode completely, a complicated after treatment must be carried out.